add option "checkSuccessful" for IMAP samplers
add STARTTLS for SMTP/LMTP samplers
add logging of STARTTLS/SSL in SMTP/LMTP samplers
fix SSL in SMTP/LMTP samplers
fix 5xx errors in IMAP samplers
fix socket leaks in IMAP/SMTP samplers
add proto_type structure
add commons-net to pom.xml